The present invention is directed to a water applicator for a paper tensile strength tester and more specifically to a water applicator for providing a controlled uniform amount of water to successive paper samples to be tested when gripped under tension in a testing machine.
Apparatus for testing the tensile strength of sheet material are old and well known in the art and are generally comprised of two, spaced-apart, gripping devices for gripping the sheet of material to be tested and pneumatic or hydraulic means for moving the two gripping devices apart until the sheet of material ruptures. The applied force at the moment of rupture can then be recorded. The Cowan U.S. Pat. No. 3,707,119 is an example of such an apparatus. The sheet of material, however, is tested in the dry condition, and no provision is made for applying water to the sheet of material to test the wet strength of the material.
The use of wet web tensile strength testing devices are also known in the art but generally are provided for testing a wet web or sheet as formed on a wire cloth. The handling of such a wet web or sheet to mount the same in a tensile strength testing machine raises a number of problems since such a wet sheet is extremely weak and easily damaged in handling. In the U.S. patent to Dauth U.S. Pat. No. 3,741,005, the wet web is formed on a Fourdrinier wire or screen. A pair of rollers are superimposed above a table supporting the Fourdrinier wire and means are provided for clamping one end of the wet web between the lower of the two rollers and the wire by the weight of the roller. By means of a suction box affixed to a movable arm, the other end of the web is lifted from the wire above the upper of the two rollers and clamped thereon by means of a spring clamping means. The rollers are then moved apart and the stress applied to the wet specimen is recorded to measure the tensile strength and elongation upon breakage of the specimen. In the Fisher et al. U.S. Pat. No. 2,893,241 the wet web or specimen is formed on a divided forming screen. One half of the screen holding the wet web is held in a fixed position and the other half of the screen is moved away from the fixed path by suitable mechanical means to apply a measured force to the wet web to measure the wet strength of the web. In both of these patents, there is no system for guaranteeing a uniform degree of wetness for the various samples to be tested, and therefore, the measured tensile strength of each specimen could vary widely depending upon the degree of wetness.